Rechargeable batteries are used in almost every aspect of daily life. A wide variety of industrial, commercial and consumer applications exist. In addition to automotive applications, larger capacity battery uses include such applications as fork lifts, golf carts, uninterruptable power supplies for protection of electronic data storage, and even energy storage for power production facilities. In the hybrid vehicle market, demand for low weight, high charge capacity batteries is rapidly increasing.
In hybrid electric vehicles (HEV), weight is a significant factor. This is particularly true in hybrid electric vehicle (PHEV) because a large component of the total weight of the vehicle is the weight of the batteries, reducing the weight of the cells is a significant consideration in designing batteries to power electric vehicles.
Current metal hydride batteries are is too heavy for PHEV application. The driving range is very limited, for example, a Toyota Prius® HEV modified by Gold Peak into a PHEV can only deliver 40 pure-electrical miles before the gasoline engine must kick in to propel the vehicle and recharge the batteries.
Current lithium-ion (Li-ion) battery technology is not mature enough to be used in vehicle applications. In its description of ongoing research efforts to develop high-power batteries for HEVs, the DOE said “High-power energy storage devices are among the critical technologies essential for the development and commercialization of HEVs.” Doe concerns with Li-ion technology include cost, performance, abuse tolerance, and calendar life:
Cost—The current cost of Li-based batteries is approximately a factor of two too high on a kW basis. The main cost drivers being addressed are the high cost of raw materials and materials processing, the cost of cell and module packaging, and manufacturing costs.
Performance—The barriers related to battery performance include a loss in discharge power at low temperatures and power fade over time and/or when cycled.
Abuse Tolerance—Many high-power batteries are not intrinsically tolerant to abusive conditions such as short circuits (including internal short circuits), overcharge, over-discharge, crush, or exposure to fire and/or other high-temperature environment.
Life—The calendar life target for hybrid systems (with conventional engines) is 15 years. Battery life goals were set to meet those targets. The 15-year calendar life is yet to be demonstrated.
Furthermore, Li-ion batteries will not be a cost-effective solution for HEVs unless manufacturing costs are slashed by 50% and for PHEVs unless manufacturing costs are slashed by 67% to 80%.
Thus, there is a need in the transportation field for a low cost, high power, high energy density, battery technology.